The present invention relates to rotary tools, especially to rotary material removing boring, milling or analogous tools. More particularly, the invention relates to improvements in drilling, boring, milling, reaming or like tools of the type wherein one or more knives are removably and adjustably mounted at the front end of an elongated support, such as a drill rod whose rear end portion can receive torque from the prime mover of a drilling, boring, milling or like machine.
It is already known to mount a clamping member for two relatively movable knife holders at the front end of an elongated rotary rod-like support. The holders are disposed in a common plane which extends at right angles to the axis of rotation of the support and are movable relative to each other substantially radially or diametrically of the support so that the knives which are mounted at their outer ends can make or finish a hole of desired diameter. As a rule, the holders are reciprocable with reference to the clamping member which is secured to the support by several clamping screws. The knives may constitute plate-like blades whose cutting edges remove material from a workpiece, or from the surface surrounding an existing bore or hole, when the support receives torque from the prime mover of the machine. The clamping member supports bolts which enable an operator to shift the two holders transversely of the axis of the support, i.e., to change the distance between the cutting edges of the two knives. When the tool is in actual use, the holders are held against movement relative to each other and relative to the clamping member by the aforementioned clamping screws which further serve to hold the clamping member against movement relative to the support.
In accordance with a presently known proposal, the front end face of the front end of the support is toothed or ribbed and is engaged by similarly toothed or ribbed rear surfaces of the two holders. The clamping member is a plate which is traversed by clamping screws extending in parallelism with the axis of rotation and meshing with the front end of the support. The holders have elongated slots which are traversed by the shanks of the clamping screws so that each holder can be shifted in the longitudinal direction of the slots in order to move the corresponding knife nearer to or further away from the other knife. The heads of the clamping screws bear against the exposed side of the plate-like clamping member which overlies the holders and urges their toothed surfaces into engagement with the toothed end face of the front end of the support. The clamping member is further formed with tapped bores for headless grub screws which extend at right angles to the axis of rotation of the support and have conical tips bearing against axially parallel surfaces of the holders. By rotating the grub screws, an operator can move the holders lengthwise of the aforementioned ribs provided that the clamping screws are sufficiently loose to reduce the bias of the clamping member upon the holders.
A drawback of the just discussed tool is that the grub screws cannot retract the respective holders, i.e., all such screws can do is to move the respective holders in a single direction. This is due to the fact that the grub screws do not mesh with but merely abut against the respective knife holders. Furthermore, the holders cannot be adjusted with reference to one another if they are detached from the support, i.e., from the clamping member which carries the grub screws. Still further, each and every adjustment of the knife holders relative to each other must be preceded by loosening of several clamping screws which normally bias the clamping member against the holders to thereby urge the toothed surfaces of the holders against the toothed end face of the front end of the support. A further drawback of the just discussed tool is that, though the holders can be shifted through considerable distances (because they partially overlap each other in their common plane), the clamping member can overlie only relatively small portions of the holders when the distance between the knives at the outer ends of the holders is increased so that the clamping force which prevents movements of the holders when the tool is in actual use must be increased proportionally with increasing diameter of the hole which is to be drilled or finished. Moreover, when the holders extend laterally beyond the clamping member, they are subjected to rather pronounced bending stresses which reduce the likelihood of the making a hole with a predictable diameter. Last but not least, the aforementioned elongated slots of the holders are exposed so that they rapidly accumulate shavings, chips and other foreign matter which interferes with adjustment of the holders relative to each other when the operator decides to move the knives nearer to or away from each other. Such entrapped foreign matter also interferes with evacuation of shavings and/or chips from the locus of removal of material by the knives, and the entrapped foreign matter is likely to effect unintentional shifting of the holders relative to each other so that the distance between the two knives changes without any initiative on the part of the operator.